First Test of Estimated Harman Target Response Curve on Various Headphones

As many of you know, Sean Olive and crew over at Harman International are developing a new target response curve for headphones. In this post I've modified InnerFidelity headphone measurements on a number of widely known headphones in order for you to have a first look at what the frequency response of headphones might look like with this new compensation curve.

The curve I used to compensate for the headphones is shown at the top of this page. The Harman curve (or a preliminary version of it) can be seen below.

I did modify the curve slightly, however. Above about 5kHz, when I used the Harman curve for compensation, I found the response in that area to be significantly elevated relative to what I hear on the various headphones. I therefore changed the curve a bit by elevating this region about 1dB to 5dB as the response moved from 5kHz to 20kHz.

I then made copies of a number of headphone measurement spreadsheets for a number of popular headphones with which enthusiasts will likely be familiar. I'd very much appreciate your feedback about the compensated frequency response plots on this page and how well they match with your listening experience.

Without further ado, I present a crude rendering of what compensated headphone frequency response plots might look like in future.

Please note that one of the reasons I did this is I'm in the midst of reviewing the Audeze LCD-X and found the sound of their headphones tipped up in the mid and upper treble more than I've experience in the past. I also had a hard time feeling they had enough bass after being exposed to the Focal Spirit Pro and NAD VISO HP50, though they're obviously well extended. Anyway, I got suckered into this rabbit hole and found the exercise illuminating and though you might feel likewise.

Wow! I'm digging the HP50 response. Also, I'm a fan of driver stabilization techniques like their shmancy ring on the outer diaphragm edge.

Wait a second... your measurement gear and Sean's are different. You need to pack up your gear and bring it to their reference room to get the curve nailed.

Remember, though, that it was a JBL room... a company known for great bass and pros at the MOAR bass fad... and some sharp treble. So, I'm not surprised at the compensation in the curve that they needed to make for headphones.

Keep this stuff up.

p.s. I tuned my EQ compenstion for my headphones to the curve as best as I could and I absolutely love it!

I should probably point out that I had read everything I could on this leading up to this article, so I have the curve quite similar to the O-W line, not Tyll's line, but I actually followed what the test subjects had done with the bass and therefor my curve does not have a +5dB bass shelf but rather a +2.5dB shelf. That's how I interpreted the data and how my ears agreed. The shelving filter is the same kind of gradual (I used 0.65 Q) with its center point at 120Hz so the curve looks like a rise starting from ~180Hz and capping around ~70Hz. Otherwise it follows the curve.

I should also point out for the sake of readers that my EQ looks nothing like the curve because my EQ is setup to compensate my AKG headphones' ear-drum measurement to follow the curve. It took some time doing math to get it right.

To me things look a little bass lite... A bit more so than what I think I heard from some of those cans. This might be due to the extra 5 dB in the bass region of the target curve. I think the bass compensation comes from perception tests, but it still seems somewhat arbitrary to me. Not sure there is a theory justification for that as there is one for the HRTF compensation for the mids and treble region.

Also, does Harman use a similar Head Accousitcs HMSIL3 measurements head/torso rig as IF?

IMHO, the golden ears FR graph is easier to interpret and feels less subjective (although it was intended to be quite a subjective review) now. I'm not sure but when one says their target compensated graph could change, it feels like he means more preference than reference. I truly hope not.

I was indded reluctant to change the curve, but when I used my closest reading of their curve above 5kHz the treble on everything was simply out of whack. But I understand your concern and agree that it's troublesome.

Basically, the raw frequency response plots (the gray set below the compensated plots) should look like the target response curve, and the compensated plot should be a flat line for a perfect headphone. SOmeday I might be able to produce plots with a target curve in the background---this time around is just a quick and dirty look at what headphones look like with a new target response curve.

Everything looks too bass light now. I like what the curves did with the treble - they seem more reflective of how I hear things. I'd say keep your original bass compensation from 300Hz below but use the Dr. Olive's curve from 300Hz up.

This is based on my own experience building speakers (two in the past year - and a dozen sitting in my parent's garage in the past twenty), and now making a lot of use of digital parametric EQ to get the right response target.

In any event, you don't know how Dr. Olive's setup is like compared to yours. It could be probably (and I suspect) that the methods used in getting a proper seal on the headphones could vary.

As we have discussed, getting the right amount of seal is a little bit of an art (not too much and not too little) with headphone measurements.

The headphone community may be used to a flat line between bass and mids as "neutral" but simple listening tests (such as online tools with test tones across the frequency range at different volumes) should be able to prove to you quite simply that they are not. Once you get close to 100hz, the tones get perceptually quiter.

In real life our tissue and bones play a huge role in the perception of low frequencies, which headphones cannot provide. Measuring of speakers and headphones does not compensate for the fact that our bodies and bones multiply the frequencies below 100hz quite considerably.

By that logic, headphone should have shelved up bass for it to sound even to us, IEMs in fact need it shelved up even higher as the outer ears, and small portion of the skull, involved in headphone listening are also removed from the equation.

People's minds adjust bass level to what they are used to, so I am sure a lot people will be up in arms about their favourite "neutral" headphones being revealed as bass light, but simple perceptual listening tests will show this is clearly the case.

I've always trusted perceptual listening tests more than I did graphs, because the two just don't match. With these new curves, they actually now look closer to what we really hear.

"In real life our tissue and bones play a huge role in the perception of low frequencies, which headphones cannot provide. Measuring of speakers and headphones does not compensate for the fact that our bodies and bones multiply the frequencies below 100hz quite considerably."

If you read the Harman papers carefully you'll find they thought this might be the case, but in further experiments they found that people were selecting about 2dB LESS bass in headphones than on speakers. Totally counterintuitive, but there you have it. None the less, I do agree that a +2 or 3dB bass boost below 120Hz is likely proper for pleasing listening.

They want less bass on speakers than headphones because when they listen to speakers the low bass is augmented by body absorption. The reason they need a boost in low bass with headphones is because that absorption is missing.

Read what Tyll said again. He said that the guys over at Harman expected that headphones would require a bass boost to sound neutral, but found that people actually found that headphones sounded neutral with 2 dB LESS bass than speakers.

What makes sense logically doesn't always work out that way in practice.

I guess personally I think the +5dB bass is a bot too much, but I do think maybe +2 or 3dB might be good. I think flat is a little bass light.

The new curve looks a LOT better to me from 1kHz to 8kHz where with my normal compensation curve regularly gives a dip in the response. So I like that a lot.

I would assume the head they use is IEC spec and sould be quite close in response to mine. But yeah, getting a seal for bass response is fairly tricky and headphone mounting proceedures definately might be a source of differences in bass response between their measurements and mine.

I'd definitely have to agree with you here, Tyll. I think +5 dB makes headphones a bit bass-lite, but +2-3 dB is probably appropriate. 1-8 KHz does seem a lot better than the previous curve, but it seems slightly elevated on the higher end. Above 8 KHz seems to be even moreso.

"I guess personally I think the +5dB bass is a bot too much, but I do think maybe +2 or 3dB might be good."

"The new curve looks a LOT better to me"

"So I like that a lot."

You seem to be swinging between being totally arbitrary and skewing your results towards where you most wish they were. I've read some of your thoughts about the limitations of objectivism in headphone analysis and so I assume I have a fair idea of your feelings about the limitations of measurements in general, but this tampered analysis is truly unhelpful. I would love to read your thoughts about how good/bad different headphones sound to you compared with how research predicts they will sound.

The +5 bass boost on Harman curve is a tricky one. On some headphones I feel the 5db of bass boost was mandatory (focal spirit pro), but on other headphones like the LCD2 and HE-400, I feel as though they extend deep down well enough without needing any bass boost whatsoever. Part of this might be the natural abilities that Planar Magnetics have in bass extension, part of it might not. Then there are some closed headphones like the M50, which are definitely way above neutral as far as bass goes. The fr graphs can only show so much, and while a closed headphone with high thd and long decay might look like it has a bass rolloff on the fr graph, it might be subjectively bass heavy.

I agree with Purrin, I say use the harman curve for the midrange and treble, while keeping your original compensation for the bass frequencies. The new midrange-treble compensation here goes better with my subjective experiences with some of these headphones as well. With this new curve applied to the midrange and treble I feel as though we can actually consider flat on your grpahs to be pretty close to flat in response.

It's not about telling people what to like. It's about establishing a new reference based on scientific research that is more relevant to the headphone listening experience than the current one. Placing the new headphone target frequency response curve on the measurement chart (as Golden Ears does with its frequency response measurements), would make it easier for the reader to compare how the measured frequency response of a headphone compares to the ideal target curve. This could be achieved without making the frequency response chart look too busy.

When we get a target resonse curve we believe in, an ideal headphone compensated would be a flat line. That's the whole point of the curve: to be able to assume ideal is a flat line and deviations from flat is a coloration. How is it hard to interpret that?

If you're talking about an ideal curve behind the uncompensated plots, that might be useful, but if I'm showing the compensated plot as well why would you need it?

If a flat line is going to represent the revised target response curve then no, you wouldn't need it. I was referring to what you've presented here for consideration and agree with I Like Headphone's comment regarding the appearance. The Golden Ears charts came to mind, which provide the reader with its target frequency response curve and the actual frequency response measurements for comparison, which I think is a helpful feature.

How does this "scientific research" ultimately differ from taking a poll, however sophisticated its method? How does majority preference demonstrate that something is ideal (or true, good, beautiful, &c.)? Why is the opinion of several men better or worse than that of one? I hope to hear some thoughtful responses because so far an ideal curve sounds like a compete boondoggle.

Harman is looking for a sound that pleases humans. The only way you can do that is to use humans as subjects. The difference between testing one and many is that we're a messy lot, and our opinions vary widely, so you have to test a lot of us to get an idea of where the center is.

The actual problem is that there is no adopted industry standard for studio speakers either, so we never know what the recording engineer was listening to when he or she mixed the music. So your thought that this whole thing is a boondogle actually misses how big a problem we have. Floyd Toole calls this something like "the circle of confusion." Sit back and relax, we're going to be watching this problem for a long time.

The main problem with Harman's study is they didn't use the recommended MUSHRA quality trial practices, only left people tweaking and recorded the result. This is broken due to various psychoacoustic reasons. (Such as getting used to a particular sound.) Plus the sample size is way too low for any conclusion.

A true quality trial would have a bunch of settings and people giving 0-5 quality scores to them, with a few so-called "anchors" - for instance: classic diffuse field target, free field target, no compensation, various modified diffuse and free fields, AM radio, cellphone.

While it is true that most IEMs and some headphones are missing a bit on subbass, their curve is starting the boost way too high - their shelf equalizer was just set this way. The upper mids are indeed bit too high to my ears - similar to original Etymotic/diffuse-field curve.

My theory about the sound is the people were comparing to speakers in a room - most rooms have standing waves in the low end - more than those tiny 2 dB they set less on speakers.

If we were to hold to high fidelity target, the real benchmark would be an accurately recorded (as in measurement microphones) live performance. This means as close to vanilla performance as possible, making any mastering issues moot.

Ideal curves are important and useful design tools but do very little to account for the endless permutations of filter arrangements present in the vast sea of human heads. Anyone that has immersed themselves in the acoustics and pyscho acoustic fields of study know very well that this mumbo-gumbo about "ideal" curves from a listening standpoint is fodder for endless debate. And if it's debate you seek to spend precious lifecycles on, then bravo, you've found your utopia. No two people perceive pure tones much less complex, dynamic frequency spectra alike. So in other words, the "ideal response curve" can not be a replacement for your own response curve. And your own response curve is anything but static or fixed; it shifts. and sometimes dramatically. This is why there are those things called Tone Controls & EQ's.

Loudness, peaking, distortion, phaseshift, tonal stack, etc all come into play and like finger prints, no two head superstructures are alike. More importantly, add to it the complex human brain and all bets are off with regard to "ideal" response curves and the perception of such therein. Recognize these variables and the pursuit of the the "ideal" becomes moot. Perhaps "ideal" guideline makes more practical sense. Perhaps not.

The perception of sound spectra fitted to some "curve du jour" (A-weight or otherwise...) doesn't matter much past the excitement of the debate. What matters is the trust you have in your own ears. Couple that trust with your best sensibilities on choosing function & comfort and viola! you have your ideal headphones. Interestingly enough, Tyll decided to massage the curves based upon his own perceptions. That alone should show you that this perception dance is "subject" to interpretation and arbitrary.

"Ideal curves" are like sea buoys; (in this instance) they give audiophiles something to home in on, a marker if you will and something perceivably tangible to debate. Don't get me wrong, points of reference are highly valuable, but just like predictive modeling in any engineering discipline, they're imperfect and changing based on a constant stream of newly discovered input variables. And in this instance, "subject" to a vast array of personal preference and opinion. So juggle me that Batman...

"Nothing has been proven to be more subjective than sound. OK, that's a bit of a stretch but you get my point." Is it ever. Is sight, touch, taste and smell any less subjective? The Snellen chart is used to test visual acuity for the general population. Optometrists test the eyes of countless individuals using standardised testing. Blood pressure, respiratory, kidney and liver function, cholesterol and blood glucose levels are all tested against standards developed for use on the general population. I'm sure that the more medically minded amongst us could cite numerous other examples. Most relevant though is the evaluation of our hearing by audiologists using standardised testing procedures. So riddle me this, what makes the development of a standardised target curve for measuring headphone frequency response any more challenging? ;)